Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $66.57   7.755%   $71.7325   $71.73   $71.75   $71.70  
  Purchase #2 $209.25   8.189%   $226.3855   $226.39   $226.40   $226.40  
  Purchase #3 $245.79   9.410%   $268.9188   $268.92   $268.90   $268.90  
  Purchase #4 $114.87   6.584%   $122.433   $122.43   $122.45   $122.40  
  Purchase #5 $210.46   3.788%   $218.4322   $218.43   $218.45   $218.40  
  Purchase #6 $45.59   7.755%   $49.1255   $49.13   $49.15   $49.10  
  Purchase #7 $99.29   4.204%   $103.4642   $103.46   $103.45   $103.50  
  7 purchase totals = $991.82       $1,060.4917   $1,060.49   $1,060.55   $1,060.40